It ended up being a heater pad wire shorted to the frame. Weird, huh?
Well, it seems that it can still lift and go backward simutaniously, just not with the handle ALL THE WAY in the far reach in the diagional corner. I'm sure the problem is right in front of me, I just can not see it.
Since the potientiometer outputs a good, steady voltage, it makes me think a setting is enabled to disable travel in reverse while lifting. But, I am the only person with the passcode to change settings here, and have not changed anything. (besides calibrations in attempt to resolve this issue)
I went to the status screen and it shows it going to neutral when the control handle is in that certain diagonal position.